1. Field of the Invention
The invention relates to a weather strip provided on a periphery of a door opening of a motor vehicle, and also relates to a method of manufacturing the weather strip.
2. Description of Related Art
Generally, a weather strip, or the like, is provided on a periphery of a door opening of a motor vehicle, such as an automobile. The weather strip includes a trim body having a substantially U-shaped cross section, and a seal portion that has a hollow shape and projects from the trim body. The trim body is fitted onto a flange provided at the periphery of the door opening so as to be held in position. A metal insert is embedded in the trim body. Holding lips are formed integrally on inside surfaces of sidewalls of the trim body, such that each holding lip extends toward the inside of the trim body. When the weather strip is mounted on the vehicle body, the trim body is fitted onto the flange and is retained in position basically utilizing the elastic force applied from the holding lips. At the time of closing the door, an edge portion of the door comes in contact with and deforms the seal portion to thereby provide a seal between the door and the vehicle body. Most of or the entire length of the weather strip thus constructed is formed by so-called extrusion molding.
In the meantime, the thickness of the flange to which the weather strip is attached may vary from one portion thereof to another. In this case, if the size (length) of each holding lip is constant over the entire circumference of the weather strip, a load (which will be called “insertion load”) required for inserting the flange into the trim body becomes large in a portion where the thickness of the flange is large, resulting in a reduced efficiency in attaching the weather strip to the vehicle body. In a portion where the thickness of the flange is small, on the other hand, the weather strip may be easily detached from the flange due to relatively small elastic force applied from the holding lips to the flange.
For preventing the above-described problems, extrusion molding for forming the weather strip may be carried out such that the projection length of each holding lip continuously varies in accordance with changes in the thickness of the flange. However, in the case where the thickness of the flange frequently changes, it is necessary to frequently change the length of each holding lip as well. Thus, the control of the length of the holding lips may become complicated, which may result in an increase in the cost. In addition, a desired projection length of the holding lip cannot be achieved if the length of the holding lip is changed with delay in relation to the thickness of the flange during extrusion molding. For avoiding this, therefore, the extrusion speed needs to be reduced to some extent, which, in turn, may result in a deterioration in the productivity or production efficiency. Still further, a certain degree of variations generally occur in the longitudinal position of the weather strip relative to the flange of the vehicle body during production and mounting of the strip on the flange. If such variations occur, the significance of precisely changing the length of the holding lip in accordance with the thickness of the flange may be lost. Namely, in the presence of the variations as described above, the weather strip may include a portion or portions in which the holding lip does not have an intended or desired projection length. In this case, the insertion load may be undesirably large.
Besides, such variations in the longitudinal position of the weather strip during production and mounting on the flange may cause the following problem. That is, when the weather strip is attached to the flange from its portion having a small thickness to its portion having a large thickness via a stepped portion between these portions, the projection length of the holding lip may be still large in a portion of the weather strip corresponding to the large-thickness portion of the flange located beyond the stepped portion. In this case, the insertion load required for inserting the flange into the weather strip may increase.
Furthermore, if the length of the holding lip is changed in accordance with the thickness of the flange as described above, the following problem may occur. That is, when the weather strip is formed into an annular shape through extrusion molding, the opposite end faces of the weather strip are bonded to each other, or the opposite end portions of the weather strip are set in a mold to be connected with each other by use of the mold molding. However, if the opposite end faces have different shapes (in this example, if the holding lip has different projection lengths at the end faces), the end faces may not be appropriately bonded to each other, or the structure of the mold used for connecting the opposite end portions of the weather strip may be undesirably complicated, causing a difficulty in connecting the end portions by using the mold.
A plurality of weather strips can be successively formed through extrusion molding. In this case, if the projection length of the holding lip is different between the leading and trailing end portions of one whether strip, an additional extruded portion, which will be wasted, is needed for allowing for a change from the length of the holding lip at the trailing end portion of the one weather strip to that at the leading end portion of the next weather strip. Consequently, the yield will be lowered and thereby the production efficiency will be decreased.